1. Field of the Invention
The present invention relates to a composite oxide for a hydrocarbon reforming catalyst for obtaining syngas, which is a gas mixture of carbon monoxide (CO) and hydrogen (H2), from hydrocarbons such as methane, and reforming agents such as water and carbon dioxide, a process for producing the catalyst, and a process for producing syngas using the composite oxide.
This application claims priority on Japanese Patent Application No. 2008-190062 filed on 23 Jul. 2008, the disclosure of which is incorporated by reference herein.
2. Description of the Related Art
When a hydrocarbon such as methane, natural gas, petroleum gas, naphtha, heavy oil or crude oil, is reacted with a reforming agent such as water, air or carbon dioxide, in a high temperature region in the presence of a catalyst, the hydrocarbon is reformed to a gas mixture containing highly reactive carbon monoxide and hydrogen. The synthesized gas mixture of carbon monoxide and hydrogen is used as a raw material for methanol, liquid fuel oil, and the like. Recently, research and development is being conducted to extract hydrogen gas for fuel cells from the gas mixture. In the synthetic reaction of the gas mixture of carbon monoxide and hydrogen, a composite oxide for a hydrocarbon reforming catalyst (hereinafter, may be simply be referred to as reforming catalyst), such as nickel/alumina and nickel/magnesia/alumina, has been used.
In the reaction system of hydrocarbon/steam using a reforming catalyst, carbonaceous particles, a reaction by-product, are likely to be deposited on the catalyst surface. The deposited carbonaceous particles cover the active sites on the catalyst surface, and lower the catalytic activity. Massive deposition of carbonaceous particles causes clogging and damaging the catalyst, and also causes the gas drifting apart from the reaction zone, and as a result, the effective proportion of the catalyst contributing to the reforming reaction decreases. Deposition of the carbonaceous particles on the catalyst surface can be prevented by introducing an excess amount of steam, but an increase in energy costs, an enlargement of facilities, and the like are unavoidable.
In order to suppress deposition of carbonaceous particles without the need to supply an excess amount of steam, reforming catalysts in which the catalytic active components are highly dispersed have been proposed (Patent Documents 1 and 2). In the descriptions in the Patent Document 1, the following method is described as a method for obtaining a reforming catalyst in which the catalytic active components are highly dispersed. A method of adding a co-precipitator to an aqueous solution of the water-soluble salts of the respective constituent elements of the catalyst particles, to thus allow hydroxides to precipitate, and carrying out primary calcination in a temperature range of 673 K to 873 K, and secondary calcination in a temperature range of 1223 K to 1573 K, is employed. In regard to the reforming catalyst described in the Patent Document 2, a porous molded body (catalyst carrier) is immersed in an aqueous solution containing catalytic active components such as Ni and Co, and additive metal components such as Mg, Al, Zr, Ti and Ca, so that the catalytic active components and the carrier constituent components are allowed to penetrate into the porous molded body. Subsequently, the porous molded body is dried, and then subjected to calcination at a high temperature of 700° C. or higher, and an activation treatment at 500° C. or higher. Then, ultramicroparticulate catalyst particles are highly dispersed in the surface layer of the porous molded body. It is described that deposition of carbonaceous particles on the catalyst surface is suppressed by the high dispersion of catalyst particles, and that an excellent catalytically active operation is maintained over a long period of time.
Patent Document 3 also describes that if use is made of a metal particle-supporting composite oxide in which metal particles as a catalyst are uniformly deposited on the surface of a composite oxide as a substrate at a high density (number of catalyst particles per unit area), a small-sized, compact reformer having high activity is obtained.    [Patent Document 1] JP-A No. 2002-126528    [Patent Document 2] JP-A No. 2004-141860    [Patent Document 3] JP-A No. 2005-103468